A very tiny bit of excellent cheese (3,5)
I believe the answer is:
top quark
'a very tiny bit' is the definition.
The definition and answer can be both natural objects as well as being singular nouns.
Perhaps there's a link between them I don't understand?
'excellent cheese' is the wordplay.
'excellent' becomes 'top' (top can mean the best).
'cheese' becomes 'quark' (I have seen 'Soft cheese ' mean 'quark' so perhaps 'cheese' could also mean 'quark').
'top'+'quark'='TOP QUARK'
'of' acts as a link.
Can you help me to learn more?
(Another definition for top quark that I've seen is " Very minor constituent".)